The purpose of this study is to find out what effect malaria in the mother has on the development of her child's immune system response to malaria and whether being exposed to malaria in the womb makes a child more likely to get malaria. The study will also assess the effect that exposure to malaria in the womb has on the child's growth and development over the first three years of life. Study participants will include 480 healthy pregnant women (greater than or equal to 15 years of age), their healthy offspring, 20 healthy people from the United States with no malaria exposure or disease and 40 adult Kenyans who have previously been exposed to malaria or have malaria with no signs of infection. Study procedures will include an ultrasound (procedure to assess the baby's growth and development in the womb), blood, urine, and stool collections. Newborns will be examined at birth, and at 6, 12, 18, 24, 30 and 36 months of age.